Wheel modules for overhead tracking sprinkler system

ABSTRACT

A horizontal sprinkler beam is supported by a plurality of ground tracking units. Each ground tracking unit includes two individual wheel modules. Various interchangeable wheel modules make possible various combinations for each ground tracking unitsimple gear motors, variable ratio drives, gear reduction mechanisms having provisions for connection to the companion drive module, and coasters. Each drive and gear module may be provided with a quick disconnect device to permit towing. Moreover, if the beam tracks circularly, each module may be provided with means for turning the wheel axes 90* whereby the towing may be endwise.

United States Patent 1 Raso et a1.

[451 Nov. 13,1973

[ WHEEL MODULES FOR OVERHEAD 4 TRACKING SPRINKLER SYSTEM [75] lnventors:Vito Raso, Buena Park; George R. Blackmore, Los Alamitos, both of 21Appl. No.: 132,679

[52] U.S. Cl 239/177, 239/212, 137/344, 180/65 F [51] Int. Cl B05b 3/12,B60k 1/02 [58] Field of Search 239/212, 213, 177; 137/344; 180/65 F [56]References Cited UNITED STATES PATENTS 3,623,662 11/1971 Reinke 239/213X 3,662,776 5/1972 Bryant et a1. 239/213 X 2,860,007 11/1958 Cornelius137/344 1,313,937 8/1919 Brinton 180/65 F 2,327,583 8/1943 Framheim180/65 R 3,587,763 6/1971 Kinkead 137/344 X 3,583,639 6/1971 C0rne1ius..239/212 2,628,863 2/1953 Maggart 239/212 X 2,729,298 1/1956 Tourneau180/65 F 3,186,506 6/1965 Leach et a1 180/65 F 3,265,147 8/1966 Coordes180/65 F 3,163,250 12/1964 Gibson 180/65 F 3,268,058 8/1966 Buckeridgeet a1. 180/65 R FOREIGN PATENTS OR APPLICATIONS 291,021 7/1967 Australia239/177 Primary Examiner-Robert S. Ward, Jr. Attorney-Flam and Flam [57]ABSTRACT 11 Claims, 14 Drawing Figures BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to ground tracking unitsfor overhead sprinkler systems.

2. Discussion of the Prior Art Overhead tracking sprinkler systems arefinding increased favor. Such systems typically incorporate a pipestring supported by a series of ground tracking units spaced from eachother perhaps by 100 feet. Each unit has a pair of tandem wheels. Eachtypical prior art ground tracking unit includes a gear motor and a pairof chain and sprocket mechanisms providing drive connections to theindividual wheels. If the terrain is quite level and if there is nosubstantial danger of traction being lost, power may be applied to onlyone of the wheels while the other coasts.

In a rectangular array, the entire pipe string sweeps back and forthover a rectangular area in a direction at right angles to the string. Ina circular array, a center is defined near one end of the pipe string.In both cases, one ground tracking unit is the lead unit operating at aset but preferably adjustable rate and the other ground tracking unitsfollow by intermittent operation to keep in proper step. i

To avoid downhill runaway, the gear mechanisms are designed to preventreverse rotation. To permit towing, it has been common to disconnect thechains from their sprockets. Disconnecting the chains from theirsprockets is also required if the wheel supports are to be turned toallow endwise towing.

Connecting and disconnecting sprocket chains is tedious. Sprocket chainsin time become rusted; they are readily fouled. Periodic maintenance isrequired. Sprockets must be attached to the wheel spindles in somepreconceived manner. As a result, each manufacture of overhead trackingsprinkler systems-has its own wheel spindle design. Lack ofstandardization complicates maintenance. Moreover, the business ofmanufacturers of overhead tracking sprinkler systems is'fluid handling,not vehicle drive systems.

' BRIEF SUMMARY OF INVENTION The primary object of this invention is toprovide a new and improved modular drive system for overhead trackingsprinklers. The inventive modular drive systems make possible importantresults: (1) maintenance of the sprinkler system as a whole is vastlysimplified and improved; (2) manufacturers of sprinkler systems need notbe concerned with the design and/or construction of drive systems or.with the design and/or construction of wheel spindles. Another object ofthe present invention is to provide a modular drive system for anoverhead tracking sprinkler system in which a right angle gear mechanismmakes possible a simple tandem drive arrangement of companion wheelmodules.

Another object of this invention is to provide a modular drive system ofthis character in which at least one of the two companion wheel modulesincorporates a worm gear or other selflocking means for preventing fordisconnecting the wheel spindle from the gear mechanism whereby towingis made possible.

Another object of this invention is to provide a mod- I ular drivesystem of this character in which, if desired,

the coupling between each module and the frame part of the groundtracking unit is so constructed and arranged as to allow selectiveorientation of the wheel axis whereby endwise towing is made possible.

In order to accomplish theforegoing objects, we provide a gear box bywhich a wheel spindle is supported. If the unit is to be a coaster unit,there are no gears in the boxflf the unit is to be a drive unit, a motoris mounted on the gear box and transmission units are appropriatelymounted in the box. If the unit is to be a motorless reducer, a jackshaft connects similar substantially coaxial gear elements of twocompanion wheel modules. All of the gear boxes are connected inprecisely the same manner to the frames of the ground tracking units.

A simple clutch mechanism disconnects the wheel spindle from the gearmechanism, there being an operating rod extending within the wheelspindle which is made hollow for this purpose.

In a specific embodiment of the invention a pin and sleeve arrangementconnects the gear box to the frame of the ground unit whereby the entiremodule is readily shifted 90 for endwise towing.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of theinvention will be made with reference to the accompanying drawings.These drawings, unless described as diagrammatic or unless otherwiseindicated, are to scale.

FIG. 1 is a diagrammatic plan view of an overhead sprinkler system ofthe circular sweep type.

FIG. 2 is a fragmentary pictorial view of a section of the sprinklerstring showing two ground tracking units, each unit incorporating amotor drive unit for one wheel, and a gear reduction unit for the otherwheel, the gear reduction unit being driven by a jack shaft connectionto the motor drive unit.

FIG. 3 is a fragmentary pictorial view showing the end ground trackingunit in which one of the wheels is reverse rotation. Accordingly, aseparate brake mecha- 4 nism need not be provided to prevent downhillrunaway. A companion object is to provide a simple means driven by avariable speed drive mechanism. ,FIGS. 4, 5, 6 and 7 are sectional viewstaken alon planescorresponding to lines 44 and 5 -5 of FIG. 2 and lines6-6 and 77 of FIG. 3.

FIG. 8 is an enlarged axialsectional view of a typical module showingthe quick-disconnect drive device.

FIG. 9 is a sectional view taken along a plan corresponding to line 99of FIG. 8.

FIG. 10 (sheet 4) is an enlarged sectional view taken along a planecorresponding to line 10--l0 of FIG. 8.

FIG. 11 is a fragmentary sectional vie similar to FIG. 8 but showing theclutch parts in disengaged position.

FIG. 12 is an enlarged transverse sectional view taken along a planecorresponding to line 12-12 of FIG. 11. Y v

FIG. 13 is a diagrammatic view illustrating the manner in which thesprinkler string may be transported.

FIG. 14 is a pictorial view of a typical vehicle unit positioned fortransport.

DETAILED DESCRIPTION The following detailed description is of the bestpresently contemplated mode of carrying out the invention.

This description is not to be taken in a limiting sense, but is mademerely for the purpose of illustrating the general principles of theinvention since the scope of the invention is best defined by theappended claims.

FIG. 1 illustrates in plan, an overhead tracking sprinkler systemcomprising an elongated beam that in this instance sweeps circularlyabout a center 13 located at one end of the beam. In the presentinstance, the sprinkler beam comprises a string of sprinkler pipe. Thepipe itself need not form the sprinkler beam, but can be supported on aseparate beam.

The beam is supported by a series of individual frames l4, l6, 18, 20,22, 24, 26 and 28 spaced along the length of the beam. Each frameextends transversely and on opposite sides of the center of gravity ofthe beam. Two wheel modules are provided for each frame, one on one sideof the beam and one on the other. The wheel modules are detachablysecured to the frames. Each module includes a wheel spindle and, if nota coaster module, then according to requirements, a gear reductionmechanism and a motor or a gear reduction mechanism together with meansfor establishing a drive connection to the companion module.

One of the two wheel modules at one end of the beam (the outer end inthe case of a radial array) is constantly driven by a variable speeddrive thus to set the traverse rate of the entire sprinkler system.Other motorized wheel modules follow the lead of the end wheel module insuch manner as to maintain proper alignment. This may be achieved, forexample, by determining requisite ON times.

It is usually desirable that power be applied to both modules of thepair in order to ensure motive power even if traction is lost at one ofthe two wheels of the pair, which may be caused, for example, by mudholes or by uneven terrain that causes one wheel to leave the ground. Itis also usually desirable to prevent coasting by connecting both wheelsthrough rear reduction mechanisms to a single motor drive.

Two intermediate ground tracking units 24 and 26 are shown in FIG. 2.Each unit'includes a horizontal frame member 30 that extendstransversely beneath the sprinkler string 10. A tetrahedral array ofbraces interconnect the stringto the corresponding member. Thus, twobraces 32 and 34 extend upwardly from spaced portions of the frame 30 toa common support collar 36 on the sprinkler string 10. Two braces 38 And40 extend upwardly from spaced portions of the frame member 30 on theopposite side to another common support collar 42.

Opposite ends of the frame 30 in this instance have bases in the form ofbearing bosses 44 and 46. The bosses are coupling members that rest uponwheel modules 48 and 50. The wheel module 48 (FIG. 4) includes a bearingbox or transmission casing 52 that supports a wheel W. The casing 52 maybe made in two parts, a hollow gear box part and a cover part suitablyregistered with each other. Projecting upwardly from and fastened to thetop of the transmission casing, is a kingpin 54 received in the bearingboss 44. The kingpin 54 is held against rotation by a locking pin 56whereby the wheel axis is located parallel to the string. A pair ofbearings 58 and 60 within the casing 52 provide cantilever support to awheel spindle 62 projecting through the front wall of the casing.

In the present instance, the wheel module 48 is motor driven.Accordingly, a motor 64 is detachably connected on the outside of therear cover part of the gear casing. The motor operates a right anglegear transmission connected to the spindle 62. A worm 66 is directlydriven by the motor and forms one element of the transmission. The worm66 is parallel to the wheel spindle 62 but laterally offset therefrom.The worm engages a worm wheel 68 mounted upon a right angle stub shaft70 located above the worm. The stub shaft 70 has its ends supported atthe side walls of the transmission casing near the top of the gearcasing. The stub shaft 70 carries a second worm 72 that engages a secondworm wheel 74 mounted upon the wheel spindle 62. The stub shaft 70 byvirtue of the arrangement of the right angle drive, extends parallel tothe direction of movement of the unit 24. By intermittently operatingthe motor 64, the truck or vehicle unit keeps in step. The reductiongearing is self-locking and thus acts to brake the module if power isremoved or if the unit tends to overrun.

The companion wheel module 50 for the ground tracking unit 24 has a gearcase 76 (FIG. 5) substantially identical to the gear case 52. The gearcase 76 mounts a wheel spindle 78 by the aid of bearings 80 and 82, allin a manner identical to the companion wheel module. The spindle 78,like the spindle 62, carries a worm wheel 84 identical to and driven inunison with the worm wheel 74. For this purpose, a jack shaft 86 (FIG.2) joins an outboard extension of the stub shaft 70 of the first wheelmodule to a similar outboard extension of a stub shaft 88 of the secondwheel module. This simple connection is made possible due to the rightangle nature of the drive whereby corresponding rotary elements oftandem wheel modules are nominally coaxial. The stub shaft 88, like thestub shaft 70, mounts a worm 90 that engages the worm wheel 84.Accordingly, the motor 64, attached only to one wheel module, drivesboth. The jack shaft 86 may be connected to the stub shaft extensions bysuitable clevis or other quick-disconnect structures. Preferably theconnections allow for certain flexure of between the cornpanion wheelmodules. Since the stub shafts 90 and 88 are above the worm 66 andspindle 62, the danger of the jack shaft interfering with the ground isminimized.

The case 76 carries a kingpin 92 received in the bearing boss 46tosupport the other end of the frame 30. A locking pin 94 holds thekingpin 92 against rotation.

FIGS. 6 and 7 show wheel module structures for the end framework unit28. One wheel module 96 is identical to the wheel module 48, except thatthe drive motor 98 incorporates a variable speed mechanism the ratio ofwhich is determined by a knob 100.

The wheel module 102 for the other end of the framework unit 28 is acoaster unit. It includes a casing 104 substantially identical to thecasings 52 and 76. Bearings 108 and 110 support a simple wheel spindle112.

The modules shown in FIGS. 4, 5, 6 and 7 can be used in any appropriatecombinations. A motorized wheel module can be used with a coaster unitor with a power take-off wheel module. The casings used for all modulesare provided with appropriate registers for mounting of motors andappropriate bosses that may be machined to accommodate bearings for theworms and stub shafts. A totally versatile arrangement is thus provided.

The sprinkler string is best moved to another field by endwise towingand as indicated diagrammatically in FIG. 13. This requires the wheelaxes to be turned 90. The modules 96 and 102 are easily turned simply byremoving the locking pins for the kingpins and rotating the kingpins 90,and thereupon reinserting the locking pins. in order to turn theinterconnected modules, such" as the modules 48 and 50, the jack shaft86 must first be disconnected, whereupon the kingpins of the units canbe relocated. If endwise towing is not required, a simpler method may beused for attaching the gear casings to the frames of the ground trackingunits. For example, the frames may provide flanges directly bolted tothe gear boxes.

The gear mechanisms of all but the coaster modules will'normally lockand prevent wheel rotation as the string is towed. To disconnect thespindles from their gear mechanisms, a simple clutch is provided asshown in FIGS. 8 through 12.

As shown in FIG. 8, the spindle 62 is connected to the hub of the wormgear 74 by the aid of clutch plate 114. The clutch plate 114 isrotatably coupled to the spindle 62 by the aid of a key or spline 116which allows the clutch plate to slide axially. The clutch plate 114 onits inner face has a set of clutch teeth 118 cooperable with a companionset of clutch teeth 120 formed on the face of the hub of the worm 74.UPon movement of the clutch plate 1 l4 outwardly, the worm 74 isdisengaged and the spindle 62 is free wheeling. However, the clutchplate 114 is normally urged inwardly into engagement by the aid of acompression spring 122.

In order to retract the clutch plate 114, an operating rod 124 isprovided. The rod is slidably accommodated in an elongated bore 126 ofthe spindle. The outer end of the operating rod mounts an eye-bracket128 by the aid of which the rod 124 may be manipulated. The inner end ofthe rod 124 is connected to the clutch plate 114 by the aid of a crossbar 130 (see also FIG. 9). The spindle has a large transverse aperture132 providing adequate clearance'for shifting movement of the cross bar130. The operating rod 124 may be held in the released or free wheelingposition of FIG. 11 by the aid of a locking pawl 134 located at theouter end of the spindle. The pawl has, a keyhole slot 136 through whichthe operating rod 124 extends and is held from moving off the rod by theenlarged shank 138 of the eyebracket. The cross bar 130 itself could beused as an element of the clutch mechanism in which case the face In theengaged position of the clutch plate (FIG. 8)

the pawl is idle. When the rod 124 is pulled out (FIG. 11), two flats140 (see also FIG. 12) on the rod 124 are in position at the end of thespindle to be interlocked by the small end of the keyhole recess 136 ofthe pawl. The clutch spring 122 tends to pull the rod back; however, the'pawl 134 now engages the end of the spindle to prevent this. The pawl134 is dished as at 142 in order to seat in the enlarged outer end 144of the bore 126. The seating of the pawl prevents accidental release ofthe rod.

The clutches are easily returned to engaged position after the stringhas been towed. Wheels are easily returned to tandem relationship.

All of the clutch parts, except the bracket 128 and pawl 134, are insidethe gear box andthus protected from mud, water, etc. A seal 146 locatedat the bottom of the enlarged bore portion 144 surrounds the rod andlimits entry of foreign materials. I

Intending to claim all novel, useful an unobvious features shown ordescribed, we make the following claims:

1. In an overhead tracking sprinkler system:

a. a sprinkler beam selectively movable in a defined path transverse tothe beam;

b. a series of individual ground tracking units spaced along the beam,each of the units including a frame extending on opposite sides of thecenter of gravity of the beam; each ground tracking unit including apair of tandem wheel modules; each wheel module of some of the groundtracking units having i. a bearing box having means detachably connectedto the corresponding frame to support the frame and to lock the bearingbox against angular movement about a vertical axis; ii. a wheel spindlesupported by bearings mounted by the box; and iii. transmission membersin said bearing box;

c. a motor for one of the wheel-modules of each of said some groundtracking units and supported on the corresponding bearing box; and

d. shaft means interconnecting the motorized wheel modules with thecompanion wheel module for powering the wheel modules in pairs by acommon motor.

2. In an overhead sprinkler system:

a. a sprinkler beam selectively movable in a circular path about acenter fixed with respect to the beam;

b. a series of individual ground tracking units spaced along the beam,each unit having a pair of coupling members spaced from each other andlocated on opposite sides of the center of gravity of the beam;

c. a pair.of wheel modules for each of the frame members, each wheelmodule having i. a bearing box having means interfitting thecorresponding coupling members to form a support for the frame memberand to lock the bearing lbox against angular movement about a vertical 7axis, l I l ii. a wheelspindle-supported by bearings mounted 'on'the'box; I g

d. said inter-fitting means and said'coupling members being adjustableto determine alternate axis orientation of said spindles in one of whichsaid axes are substantially parallelto said sprinkler beam for angulartracking movement of said sprinkler beam, and in the other of which saidaxes extend substantially at right angles to said beam for endwisetowing of said beam;

e. one of each pair of wheel modules having a gear reduction mechanismmounted in its bearing box and connected to the corresponding spindle;

f. said motor being attached to thecorresponding bearing boxindependently of the corresponding frame;

g. some of the other said pairs of wheel modules having a gearreductionmechanism mounted in its bearing box and connected to thecorresponding spindle; and

h. a jack shaft interconnecting corresponding parts of the transmissionmechanisms of the companion wheel modules whereby both wheel modules arepowered by a common motor.

3. The combination as set forth in claim 2 together withquick-disconnect clutch mechanisms for freeing the wheel spindles ofthose wheel modules provided with gear reduction mechanisms to permitcoasting thereof for towing purposes.

4. In an overhead tracking sprinkler system:

a. a sprinkler beam selectively movable in a defined path transverse tothe beam; b. a series of individual ground tracking units spaced alongthe beam, each of the units including a frame extending on oppositesides of the center of gravity of the beam; each ground tracking unitincluding a pair of tandem wheel modules; each wheel module of some ofthe ground tracking units having i. a bearing box having meansdetachably connected to the corresponding frame to support the frame andto lock the bearing box against angular movement about a vertical axis;

ii. a wheel spindle supported by bearings mounted by the box; and

iii. transmission members in said bearing box including a rotary elementhaving a substantially horizontal axis orientation extendingsubstantially parallel to the direction of traverse of said sprinklerbeam;

c. a motor for one of the wheel modules of each of said some groundtracking units and supported on the corresponding bearing box; and

d. the said rotary elements of companion tandem wheel modules beingsubstantially coaxial, there being a jack shaft interconnecting saidcorresponding rotary elements of tandem wheel modules.

5. A wheel module for use with an overhead tracking sprinkler systemhaving a sprinkler beam selectively movable in a circular path about acenter fixed with respect to the beam, and having asupporting frameproviding a series of bases located on both sides of the center ofgravity of the beam and located in spaced relationship along the. lengthof the beam, including:

a. a bearing box;

b. a coupling member on the box detachably cooperable with any one ofsaid bases to support said base and to hold the bearing box againstangular movement about a vertical axis;

c. a wheel spindle supported by bearings mounted in the box;

d. said coupling member and said base being relatively adjustable todetermine alternate axis orien tation of said spindle in one of whichsaid axes is substantially parallel to said sprinkler beam for angulartracking movement thereof, and in the other of which said axes extendssubstantially at right angles to said beam for endwise towing thereof;

e. a stub shaft having an axis extending in a plane perpendicular to theaxis of said spindle;

a pair of gear elements carried by said stub shaft,

one being cooperable with the motor mounted on the box for rotating'thestub shaft, and the other being cooperable with a companion gear elementcarried on said spindle; and

g. a jack shaft for connecting said stub shaft to the aligned stub shaftof a like wheel module located on the opposite side of the sprinklerbeam.

6. In an overhead tracking sprinkler system: a. a sprinkler beamselectively movable in a defined path transverse to the beam; b. aseries of individual ground tracking units spaced along the beam, eachof the units including a frame extending transversely on opposite sidesof the center of gravity of the beam; each ground tracking unitincluding a pair of generally tandem wheel modules; each module havingi. a bearing box having means detachably connected to the correspondingframe and supporting the frame; and

ii. a wheel spindle supported by bearings mounted by the box;

one of the wheel modules of some of the ground tracking units includinga motor carried by the bearing box for moving the corresponding wheelspindle to impart movement of said beam in its path, some of said wheelmodules including gear reduction mechanisms of the self-locking type;and

c. quick-disconnect clutch means between the gear reduction mechanismsand the corresponding wheel spindles for freeing the wheel spindles ofthose modules provided with gear reduction mechanisms.

7. The combination as set forth in claim 6 in which the motor isdetachably mounted on the outside of the corresponding gear box.

8. The combination as set forth in claim 6 in which said clutch means islocated internally of said box and in which said clutch means has anexternally accessible actuator.

9. The combination as set forth in claim 6 in which each of said gearreduction mechanisms includes a gear element for the correspondingspindle; said quickdisconnect clutch means including an axiallyseparable coupling between the spindle and said gear element, springmeans normally urging said axially separable coupling into engagedposition and an operating rod extending through a bore in the spindleand having one end accessible at the outer end of the spindle, andhaving its other end connected to said coupling for causing saidcoupling to be disengaged upon axial movement of said operating rodagainst the force of said spring means; and a locking mechanism forreleasably holding said operating rod in coupling disengaged position.

10. The combination as set forth in claim 9 in which said lockingmechanism comprises a locking key or pawl located at the outer end ofsaid rod and retained on the end of said rod by a stop on said rod, saidkey having a slot movable to engage grooves on opposite sides of saidrod upon transverse movement of said key or pawl when said grooves aremoved into longitudinal alignment with the end of said spindle wherebythe interference between said pawl or key and the end of said spindleholds said rod in'coupling disengaged position.

11. The combination as set forth in claim 10 in which the end of saidspindle has an enlarged recess through which said rod extends, said keyor pawl having a dished portion positioned to seat at the end of saidrecess when coupled to said rod whereby said pawl or key is protectedfrom accidental dislodgment from said rod. l

1. In an overhead tracking sprinkler system: a. a sprinkler beamselectively movable in a defined path transverse to the beam; b. aseries of individual ground tracking units spaced along the beam, eachof the units including a frame extending on opposite sides of the centerof gravity of the beam; each ground tracking unit including a pair oftandem wheel modules; each wheel module of some of the ground trackingunits having i. a bearing box having means detachably connected to thecorresponding frame to support the frame and to lock the bearing boxagainst angular movement about a vertical axis; ii. a wheel spindlesupported by bearings mounted by the box; and iii. transmission membersin said bearing box; c. a motor for one of the wheel modules of each ofsaid some ground tracking units and supported on the correspondingbearing box; and d. shaft means interconnecting the motorized wheelmodules with the companion wheel module for powering the wheel modulesin pairs by a common motor.
 2. In an overhead sprinkler system: a. asprinkler beam selectively movable in a circular path about a centerfixed with respect to the beam; b. a series of individual groundtracking units spaced along the beam, each unit having a pair ofcoupling members spaced from each other and located on opposite sides ofthe center of gravity of the beam; c. a pair of wheel modules for eachof the frame members, each wheel module having i. a bearing box havingmeans interfitting the corresponding coupling members to form a supportfor the frame member and to lock the bearing box against angularmovement about a vertical axis, ii. a wheel spindle supported bybearings mounted on the box; d. said interfitting means and saidcoupling members being adjustable to determine alternate axisorientation of said spindles in one of which said axes are substantiallyparallel to said sprinkler beam for angular tracking movement of saidsprinkler beam, and in the other of which said axes extend substantiallyat right angles to said beam for endwise towing of said beam; e. one ofeach pair of wheel modules having a gear reduction mechanism mounted inits bearing box and connected to the corresponding spindle; f. saidmotor being attached to the corresponding bearing box independently ofthe corresponding frame; g. some of the other said pairs of wheelmodules having a gear reduction mechanism mounted in its bearing box andconnected to the corresponding spindle; and h. a jack shaftinterconnecting corresponding parts of the transmission mechanisms ofthe companion wheel modules whereby both wheel modules are powered by acommon motor.
 3. The combination as set forth in claim 2 together withquick-disconnect clutch mechanisms for freeing the wheel spindles ofthose wheel modules provided with gear reduction mechanisms to permitcoasting thereof for towing purposes.
 4. In an overhead trackingsprinkler system: a. a sprinkler beam selectively movable in a definedpath transverse to the beam; b. a series of individual ground trackingunits spaced along the beam, each of the units including a frameextending on opposite sides of the center of gravity of the beam; eachground tracking unit including a pair of tandem wheel modules; eachwheel module of some of the ground tracking units having i. a bearingbox having means detachably connected to the corresponding frame tosupport the frame and to lock the bearing box against angular movementabout a vertical axis; ii. a wheel spindle supported by bearings mountedby the box; and iii. transmission members in said bearing box includinga rotary element having a substantially horizontal axis orientationextending substantially parallel to the direction of traverse of saidsprinkler beam; c. a motor for one of the wheel modules of each of saidsome ground tracking units and supported on the corresponding bearingbox; and d. the said rotary elements of companion tandem wheel modulesbeing substantially coaxial, there being a jack shaft interconnectingsaid corresponding rotary elements of tandem wheel modules.
 5. A wheelmodule for use with an overhead tracking sprinkler system having asprinkler beam selectively movable in a circular path about a centerfixed with respect to the beam, and having a supporting frame providinga series of bases located on both sides of the center of gravity of thebeam and located in spaced relationship along the length of the beam,including: a. a bearing box; b. a coupling member on the box detachablycooperable with any one of said bases to support said base and to holdthe bearing box against angular movement about a vertical axis; c. awheel spindle supported by bearings mounted in the box; d. said couplingmember and said base being relatively adjustable to determine alternateaxis orientation of said spindle in one of which said axes issubstantially parallel to said sprinkler beam for angular trackingmovement thereof, and in the other of which said axes extendssubstantially at right angles to said beam for endwise towing thereof;e. a stub shaft having an axis extending in a plane perpendicular to theaxis of said spindle; f. a pair of gear elements carried by said stubshaft, one being cooperable with the motor mounted on the box forrotating the stUb shaft, and the other being cooperable with a companiongear element carried on said spindle; and g. a jack shaft for connectingsaid stub shaft to the aligned stub shaft of a like wheel module locatedon the opposite side of the sprinkler beam.
 6. In an overhead trackingsprinkler system: a. a sprinkler beam selectively movable in a definedpath transverse to the beam; b. a series of individual ground trackingunits spaced along the beam, each of the units including a frameextending transversely on opposite sides of the center of gravity of thebeam; each ground tracking unit including a pair of generally tandemwheel modules; each module having i. a bearing box having meansdetachably connected to the corresponding frame and supporting theframe; and ii. a wheel spindle supported by bearings mounted by the box;one of the wheel modules of some of the ground tracking units includinga motor carried by the bearing box for moving the corresponding wheelspindle to impart movement of said beam in its path, some of said wheelmodules including gear reduction mechanisms of the self-locking type;and c. quick-disconnect clutch means between the gear reductionmechanisms and the corresponding wheel spindles for freeing the wheelspindles of those modules provided with gear reduction mechanisms. 7.The combination as set forth in claim 6 in which the motor is detachablymounted on the outside of the corresponding gear box.
 8. The combinationas set forth in claim 6 in which said clutch means is located internallyof said box and in which said clutch means has an externally accessibleactuator.
 9. The combination as set forth in claim 6 in which each ofsaid gear reduction mechanisms includes a gear element for thecorresponding spindle; said quick-disconnect clutch means including anaxially separable coupling between the spindle and said gear element,spring means normally urging said axially separable coupling intoengaged position and an operating rod extending through a bore in thespindle and having one end accessible at the outer end of the spindle,and having its other end connected to said coupling for causing saidcoupling to be disengaged upon axial movement of said operating rodagainst the force of said spring means; and a locking mechanism forreleasably holding said operating rod in coupling disengaged position.10. The combination as set forth in claim 9 in which said lockingmechanism comprises a locking key or pawl located at the outer end ofsaid rod and retained on the end of said rod by a stop on said rod, saidkey having a slot movable to engage grooves on opposite sides of saidrod upon transverse movement of said key or pawl when said grooves aremoved into longitudinal alignment with the end of said spindle wherebythe interference between said pawl or key and the end of said spindleholds said rod in coupling disengaged position.
 11. The combination asset forth in claim 10 in which the end of said spindle has an enlargedrecess through which said rod extends, said key or pawl having a dishedportion positioned to seat at the end of said recess when coupled tosaid rod whereby said pawl or key is protected from accidentaldislodgment from said rod.